Nitinol is a nickel-titanium intermetallic compound invented at the Naval Ordinance Laboratory in the early 1960's. It is a material with useful properties, but manufacturers who have worked with it have had little success in making Nitinol parts and semi-finished forms. Because Nitinol is so extremely difficult to form and machine, workers in the metal products arts usually abandoned the effort to make products out of anything except drawn wire because the time and costs involved did not warrant the paltry results they were able to obtain.
The most commonly used kinds of Nitinol are superelastic and shape memory Type 55 Nitinol, an intermetallic compound having 55% nickel and 45% titanium by weight. Superelastic Nitinol achieves its properties of high elastic elongation by processes including substantial cold working. It is used almost exclusively in the form of wire, the drawing of which imparts the cold working.
Type 60 Nitinol is an intermetallic compound having 60% Nickel and 40% Titanium by weight. It has many properties that have been unrecognized as of potential value. It can be polished to an extremely smooth finish, less than 1 microinch rms. It is naturally hard and can be heat treated to a hardness on the order of 62Rc or higher. It can be processed to have a very hard integral ceramic surface that can itself be polished to an even smoother surface than the parent metal. It is non-magnetic, immune to corrosion from most common corrosive agents, and has high yield strength and toughness, even at elevated temperatures. It is 26% lower density than steel for weight sensitive applications such as aircraft, satellites and spacecraft. However, there has hitherto been little effort in making useful parts out to Nitinol because it is so difficult to work, because it was known to be brittle, and because there has been no known method to make parts and forms out of Type 60 Nitinol.
In my co-pending application Ser. No. 09/879,371, the disclosure of which is incorporated by reference herein, I describe a process for imparting properties, unknown until my discovery thereof, of high elasticity, toughness, and shape memory effect to Type 60 Nitinol. I have, since the filing of that application, refined the processes and made additional discoveries that enable the tailoring of the transition temperature of the shape memory effect in Type 60 Nitinol. I have also discovered that ultraelastic Type 60 Nitinol is itself a shape memory effect material with a very low transition temperature. The range and value of the applications of these materials are beyond imagination.